The present invention relates broadly to radar receiver protectors, and in particular to an RF-primed high power halogen vial receiver protector apparatus.
At microwave frequencies, the mixer which is the input circuit to a radar receiver is very susceptible to damage by large applied signals, and therefore must be carefully protected. This sensitivity to damage is especially true of crystal mixers which are generally utilized in radar receiver. In the prior art, receiver protective system has been disclosed that are particularly applicable to radar systems wherein the receiver and transmitter are connected to the same antenna, thus making it necessary to protect the receiver during the interval of time when the transmitter is in operation. It is also necessary to protect the radar receiver when it is near some other transmitter, such as, for example, another radar that is operating at nearly the same frequency, because the adjacent transmitter may impress a signal of a sufficient amplitude to injure the radar receiver.
Practically all modern day radar systems utilize a duplexing section which contains a T-R switch to permit the use of a single antenna for both transmitting and receiving. Generally, the T-R switches comprise some type of gas discharge tube. If the gas discharge tube is fired by a pulse which is derived from the transmitted signal, a small amount of power may get into the mixer section of the receiver prior to ignition of the gas discharge tube by the transmitter derived pulse. In order to prevent this situation, prepulsing systems have been employed.
One of the problems associated with high power vial stages used in waveguide receiver protectors is the lack of stable breakdown. This is mainly due to the absence of free electron priming or a keepalive. Since vial stages primarily use halogen gases to achieve a fast recovery period under the incidence of very high microwave power, the use of metallic keepalive electrodes is precluded. This is true because halogens will react with all metals to form metallic halides. Thus, the gases will adhere to the electrode surfaces and will materially decrease the operating pressures within the vial that will cause the stage to fail. Since the vial stage is always in the high power rf input stage, gas cleanup is a critical factor in its operating lifetime. The present invention provides an RF-primed high power halogen vial apparatus which utilizes a unique method to obtain free electrons (keepalive) in the vial stage without introducing metal electrodes to the halogen gas. In this manner, a first pulse breakdown will occur and the gas discharge will occur repeatedly early in the incident rf pulse waveform without undergoing a statistically-varying formative time lag.